13:45 〜 14:00
[MIS05-06] Beryllium isotope records from sectors of the West and East Antarctic Ice sheet reveal Holocene melting related to the incursion of Circumpolar Deep Water
キーワード：Beryllium isotopes, Holocene, Antarctica, Glacial discharge
Glaciers and ice sheets in both mountain regions and the poles are losing mass, causing an increase in the rate of mean sea level rise whilst expanding an ever-warming ocean. Sea level rose globally by ~15 cm over the past ~100 years but that rate is currently accelerating, becoming twice as fast (3.6 mm yr-1). Sea level rise could reach around 30 to 60 cm by 2100 if greenhouse gas emissions are sharply reduced and global warming is limited less than 2°C but could rise to around 60 to 110 cm if greenhouse gas emissions continue to increase [1]. It is therefore imperative for Earth scientists to use the geological record to reconstruct the deglacial history of key regions relevant to sea level rise during past periods of extreme climate [e.g., 2]. This will allow better constraints on numerical models for future climate predictions and a greater understanding of the cryosphere response to future global warming. Here, we present the authigenic Be isotope composition of lake and marine sediments from the Lützow-Holm Bay and the Ferrero Bay, respectively [3-5].
Meteoric 10Be is produced in the atmosphere by cosmic rays and delivered to the Earth and ocean surface via dust and precipitation. In Antarctica, these sources of 10Be become locked up in ice sheets and are subsequently released to the continental shelf during periods of melting and freshwater discharge, where they adhere to suspended particles in the water column and subsequently accumulate on the basin floor [6]. Stable 9Be is present in silicate rocks and is released during subglacial weathering, with little simultaneous release of 10Be, and transported to the oceans via meltwater outflow [7]. When Be is incorporated into the authigenic phase of marine sediments, the 10Be/9Be reflects that of the overlying water column [8], which in turn reflects the relative dominance of freshwater flux and/or subglacial weathering.
New Be isotope records from Lakes Maruwan Oike and Lake Skallen, near Lützow-Holm Bay, and Ferrero Bay, the Amundsen Sea Embayment, reveal a large increase in 10Be abundance and 10Be/9Be ratios between 4.1 to 3.6 Ka BP and 10 to 6 ka BP, respectively. This suggests widespread meltwater discharge and destabilisation of respective parts of the East and West Antarctic Ice Sheet during the Late and Early Holocene. Such events could be linked to a strengthening of the Southern Hemisphere westerlies which, in turn, would have caused enhanced upwelling of warm Circumpolar Deep Waters (CDW) onto the shelf leading to increased marine ice shelf instability and melting [9, 10] suggesting possible Antarctic contribution to global sea-level rise during the Holocene [11].
[1] Pörtner H.-O. et al. (2019) IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. [2] Mackintosh et al. (2014) Quaternary Science Reviews 100: p 10-30. [3] Takano, Y., et al. (2015) Progress in Earth and Planetary Science 2(1): p. 8. [4] Takano, Y., et al. (2012) Applied Geochemistry 27(12): p. 2546-2559. [5] Minzoni, R.T., et al. (2017) The Holocene 27(11): p. 1645-1658. [6] Simon, Q., et al. (2016) Quaternary Science Reviews 140: p. 142-162. [7] Sjunneskog, C. et al. (2007) Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 259(1): p. 576-583. [8] von Blanckenburg, F. and J. Bouchez (2014) Earth and Planetary Science Letters 387: p. 34-43. [9] Crosta, X., et al. (2018) Global & Planetary Change 166: p. 62-74.
[10] Yokoyama, Y., et al. (2016) Proceedings of the National Academy of Sciences 113(9): p. 2354. [11] Yokoyama, Y., et al. (2019) Quaternary Science Reviews 206: p. 150-161.
Meteoric 10Be is produced in the atmosphere by cosmic rays and delivered to the Earth and ocean surface via dust and precipitation. In Antarctica, these sources of 10Be become locked up in ice sheets and are subsequently released to the continental shelf during periods of melting and freshwater discharge, where they adhere to suspended particles in the water column and subsequently accumulate on the basin floor [6]. Stable 9Be is present in silicate rocks and is released during subglacial weathering, with little simultaneous release of 10Be, and transported to the oceans via meltwater outflow [7]. When Be is incorporated into the authigenic phase of marine sediments, the 10Be/9Be reflects that of the overlying water column [8], which in turn reflects the relative dominance of freshwater flux and/or subglacial weathering.
New Be isotope records from Lakes Maruwan Oike and Lake Skallen, near Lützow-Holm Bay, and Ferrero Bay, the Amundsen Sea Embayment, reveal a large increase in 10Be abundance and 10Be/9Be ratios between 4.1 to 3.6 Ka BP and 10 to 6 ka BP, respectively. This suggests widespread meltwater discharge and destabilisation of respective parts of the East and West Antarctic Ice Sheet during the Late and Early Holocene. Such events could be linked to a strengthening of the Southern Hemisphere westerlies which, in turn, would have caused enhanced upwelling of warm Circumpolar Deep Waters (CDW) onto the shelf leading to increased marine ice shelf instability and melting [9, 10] suggesting possible Antarctic contribution to global sea-level rise during the Holocene [11].
[1] Pörtner H.-O. et al. (2019) IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. [2] Mackintosh et al. (2014) Quaternary Science Reviews 100: p 10-30. [3] Takano, Y., et al. (2015) Progress in Earth and Planetary Science 2(1): p. 8. [4] Takano, Y., et al. (2012) Applied Geochemistry 27(12): p. 2546-2559. [5] Minzoni, R.T., et al. (2017) The Holocene 27(11): p. 1645-1658. [6] Simon, Q., et al. (2016) Quaternary Science Reviews 140: p. 142-162. [7] Sjunneskog, C. et al. (2007) Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 259(1): p. 576-583. [8] von Blanckenburg, F. and J. Bouchez (2014) Earth and Planetary Science Letters 387: p. 34-43. [9] Crosta, X., et al. (2018) Global & Planetary Change 166: p. 62-74.
[10] Yokoyama, Y., et al. (2016) Proceedings of the National Academy of Sciences 113(9): p. 2354. [11] Yokoyama, Y., et al. (2019) Quaternary Science Reviews 206: p. 150-161.